FormatXTC: add wavelength_fallback parameter

If the wavelength cannot be found from the XTC stream, fall back to using this value instead

Also fixes some serialtbx imports

newsfragments/XXX.misc

@@ -0,0 +1 @@
+XTC support: add wavelength_fallback parameter

src/dxtbx/format/FormatXTC.py

@@ -68,6 +68,10 @@
             for any events with a dropped spectrum. If the spectrum is \
             present and calibration constants are provided, \
             wavelength_offset is ignored.
+  wavelength_fallback = None
+    .type = float
+    .help = If the wavelength cannot be found from the XTC stream, fall \
+            back to using this value instead
   spectrum_address = FEE-SPEC0
     .type = str
     .help = Address for incident beam spectrometer
@@ -391,7 +395,7 @@ def get_psana_timestamp(self, index):
         sec = time[0]
         nsec = time[1]
 
-        return serialtbx.util.timestamp((sec, nsec / 1e6))
+        return serialtbx.util.time.timestamp((sec, nsec / 1e6))
 
     def get_num_images(self):
         return self.n_images
@@ -416,6 +420,8 @@ def _beam(self, index=None):
                 wavelength = serialtbx.detector.xtc.evt_wavelength(
                     evt, delta_k=self.params.wavelength_delta_k
                 )
+                if wavelength is None or wavelength <= 0:
+                    wavelength = self.params.wavelength_fallback
                 if self.params.wavelength_offset is not None:
                     wavelength += self.params.wavelength_offset
             if wavelength is None:

src/dxtbx/format/FormatXTCJungfrau.py

@@ -64,7 +64,7 @@ def understand(image_file):
         return any(["jungfrau" in src.lower() for src in params.detector_address])
 
     def get_raw_data(self, index=None):
-        from serialtbx.detector.util import jungfrau
+        from serialtbx.detector import jungfrau
 
         if index is None:
             index = 0